1. Field of the Invention
The invention concerns a system for the analysis of sample liquids, comprising test elements, a moisture-impermeable, tightly sealable storage container for at least two test elements and a measuring instrument that is independent of a power supply network and can be held with one hand. The invention also concerns a method for the determination of an analyte in a sample liquid.
2. Description of the Related Art
Analytical elements that allow the determination of individual parameters in sample liquids have been known for some time and a great variety of them are commercially available. In particular, systems are available for the fields of medical diagnostics and environmental analysis which can also be operated by persons with little training. Those systems are simple to operate which do not require the use of liquid reagents and in which preparation of the sample material is in general unnecessary or can be accomplished in an uncomplicated manner. A "dry chemistry" was developed for such so-called rapid tests where the water contained in the sample liquid serves alone as the solvent.
For example, systems are commonly used to determine glucose in blood in which the patient applies small amounts of freshly collected blood to a test strip and carries out the measurement using an instrument that can be operated simply, for example a reflection photometer. In analytical systems of the most common prior art, the test elements are present separately outside the measuring instrument and are only inserted into the measuring instrument for the actual measurement process.
Conventional measuring instruments have an opening, for example a slit, in which a test strip can be inserted by hand. Guiding elements ensure that a test strip is inserted in the intended orientation. Constructive features of the instrument must be present to ensure the desired positioning of the test strip. This is usually achieved by a stop which prevents insertion beyond a predetermined target position.
Although recently more and more systems based on electrochemical sensors have been offered for sale, the most common systems use analytical tests which are based on color changes that are exhibited during the course of the detection reaction when analytes to be determined are present. Detection of the color change occurring on the test strip can be carried out by reflection photometry. A transmission measurement is also possible but requires at least partially transparent test strips. The devices that are necessary for the photometry for generating and detecting radiation are in principle known in the prior art.
Test strips of the prior art have a test zone and a holder for this test zone usually in the form of a stiff foil which enables a comfortable and safe handling of the test strip. The test zone itself can be composed of several layers. Layers of fleece materials are for example usual for determining analytes in blood which separate cellular components from serum. In addition, layers are commonly used in which reactions take place or which contribute to the dosing of the sample material. Typical structures of test strips are for example described in the German Patent Applications DE 196 296 56.0 and DE 196 296 57.9 and in EP-B 0 271 854, EP-A-0 487 068, WO 92/17768 and DE-A 195 23049.
Only in a few cases is the analyte detected by reaction of the analyte with a single substance to directly form a dye. Usually, a chain of chemical and/or biochemical reactions occurs which finally lead to an observable change in color. The test zone on which the color reaction can be observed must have a size and shape that ensures a zone of constant size is irradiated or radiated even with the manufacturing tolerances of the measuring instrument and test element.
Test elements known from the prior art essentially have the shape of a flat strip or a flat rectangular plate. Paper and in particular cardboards and plastics are commonly used as materials. The test zone is either applied to the said materials by impregnation of the material with the corresponding reagents or in the form of additional layers.
The storage stability of many test elements is greatly reduced by the influence of moisture, for example, from the ambient air since the test zones often contain sensitive, usually biochemical reagents. For this reason, commercially available test elements are either individually sealed or are provided in large amounts packaged in special containers. Sealing is usually carried out in plastic laminated metal foils, preferably aluminum laminates. This packaging form is used above all for rapid tests that are to be evaluated by an instrument or visually. In order to use a sealed test element, the packaging is torn open manually and the test element is removed. In the case of test strips which have to be used more frequently by the user, for example blood glucose test strips for diabetics, several of them are usually present in re-sealable containers made of moisture-impermeable materials which can also contain desiccants to absorb moisture that has entered.
The measurement process with the said systems for analysis with dry chemistry rapid tests is carried out using an analytical instrument and separate test strips for single use. For this the user of the system manually opens a storage container, removes a test strip and closes the container again in order to protect the remaining test strips in the storage container from moisture. Afterwards, the sample liquid to be analysed is applied to the sample application zone of the test strip. The test strip is inserted into the analytical instrument either directly after sample application or after an incubation period. In more modern systems, the sample application does not take place until the test strip is in the instrument. In both procedures, the test strip is inserted manually into the measuring instrument by the operator. The positioning of the test strip is ensured by constructive measures.
The actual measurement process is usually started by the operator's act of pressing a button. There are also systems in which the measurement process is started automatically when the test strip is inserted into the instrument. After completion of the measurement which the user sees on the instrument display, the analytical process is ended by removing the test strip.
A disadvantage of the described systems for analysing sample liquids is that the operator usually has to carry out several handling steps with the test elements. Since the users of such systems, particularly in the field of medical diagnostics, are often diabetics which have great difficulty in safely handling small test elements, there is a need to construct analytical systems which do not require the handling of individual test elements or reduces this to a minimum.
A further disadvantage of current systems is the manual positioning of the test strips by the operator which does not reliably prevent operating errors. Consequently, attempts are made to provide systems in which the test elements are positioned in such a way that operating errors that are due to improper positioning are reliably avoided.
Since the test strips which are used in the common systems exhibit manufacturing tolerances in their detection characteristics, a correct evaluation requires the transmission of batch-specific characteristic data to the measuring instrument. Nowadays, batch codes are often used for this which are either directly mounted on the test strips and are automatically registered when the strip is inserted into the instrument or they are present on the packaging of the test strips and have to be entered manually by the operator for example by means of a keyboard. Both variants are not an optimal solution. In order to code the individual test strips, the manufacturer must first randomly analyse the functional characteristics before the strips can be provided with a code. Hence, the production process cannot be completed in one step which makes the process complicated and ultimately expensive. If in contrast the package is furnished with the code, the production process can indeed be completed before the coding but errors may occur when the code is transmitted manually from the package to the instrument for example by false or erroneous input by the operator. Therefore, the aim is to optimize the code transmission.
The object of the present invention was to eliminate the disadvantages of the prior art.
This is achieved by the subject matter of the invention as characterized in the patent claims.